Vertical inductive thin film heads have evolved considerably during the last decade, and are now a well proven concept with many established advantages over conventional head designs. Two distinct structures have evolved, upon which most current designs are based. The two structures differ in the way the thin film electrical turns are fabricated around a yoke structure. In one arrangement, the electrical coil is deposited in a spiral pattern, and in the other arrangement the coil is formed in the shape of a helix. Both prior art techniques severely limit the number of turns which can be fabricated through the yoke.
A typical prior art thin film magnetic head assembly employing the spiral technique is disclosed in the Church et al U.S. Pat. No. 4,219,854 issued Aug. 26, 1980. The spiral structure is essentially a planar configuration with the spiral coil being deposited on a single level. The pole pieces are spaced above and below the thin film coil and because of this close proximity of the pole pieces, the magnetic efficiency is inherently low. The magnetic efficiency is further degraded in a manner directly proportional to the number of turns through the yoke structure because the magnetic efficiency varies as l/L where l is the distance between the pole pieces and L is the distance between the back leg of the core arrangement and the gap. Another problem with the spiral technique is that the turns extend beyond the track width. Increasing the number of turns causes lateral spread of the head assembly, which is a limiting factor in head per track devices where high track density is desired. However, an advantage of spiral heads is that fabrication of the thin film coil is accomplished with relative ease.
The helix is a multi-layer structure. The conductor is deposited sequentially with appropriate insulation. A typical prior art helical coil arrangement is disclosed in the Gibson U.S. Pat. No. 4,143,458 issued Mar. 13, 1979. The helical arrangement offers some improved magnetic efficiency over the spiral arrangement but only at the expense of severe processing problems encountered during deposition and definition of the multiple layers.
These presently known thin film head designs do not permit both high magnetic efficiency and ease of fabrication. Although the spiral head is easy to fabricate, it it limited in the number of turns which can be accomodated if close track spacing is desired. The resultant device will have fewer turns and thus the efficiency will be low. In the present invention a large number of turns are easily manufactured and do not effect the magnetic efficiency or increase difficulties in processing. A head using the helical coil arrangement has better magnetic efficiency and is more narrow so as to permit closer spacing, but such heads are difficult to fabricate.